From the prior art, it is known for a setpoint value for the position of the adjustment device to be predefined at the regulating valve and for travel or force feedback of the position of the adjustment device (for example of the actuation cylinder) to the regulating valve to be provided. In this way, during an adjustment, the regulating valve is influenced such that, when the desired position is reached, it returns to its neutral position again in which the actuation cylinder is separated from the actuation pressure medium source and from the actuation pressure medium sink.
Documents DE 100 01 826 C1 and DE 199 49 169 C2 present regulating valves of said type whose housings are each in the form of cartridges and whose respective longitudinal axis coincides with the longitudinal axis of an actuation piston of the actuation cylinder. In this case, feedback of the travel of the actuation piston is realized, which is converted into a force by means of an interposed spring.
In the case of pressure regulation arrangements for adjustable hydrostatic pumps known from the prior art, the pressure regulating valve is connected to the high-pressure side of the pump to be regulated, in order to detect the pump pressure thereof and “feed back” said pump pressure to the pressure regulating valve. In this case, the pump pressure on the valve body of the pressure regulating valve acts counter to a spring in the direction of a reduction of the delivery volume.
Furthermore, the actuation pressure medium which is required for the supply to the adjustment device of the pump and which is controlled by the pressure regulating valve can be picked off from the working line of the pump and supplied via the pressure regulating valve to the actuation cylinder in a manner dependent on the desired adjustment of the pump.
The applicant's publication RD 9 2711/01.12 A10VSO presents, on page 11/48, a pressure regulating valve of said type with feedback of the working pressure of the pump to be regulated. The pressure regulating valve acts as a pressure limiter for the working pressure of the pump. For this purpose, a spring acts on the valve body of the pressure regulating valve in the direction of an increase of the delivery volume of the pump. The maximum working pressure of the pump can be set by way of a preparatory adjustment of the preload of the spring.
The same publication from the applicant presents, on page 15/48, a pressure regulating valve arrangement in which, in addition to the main pressure regulating valve, an electrically adjustable pressure limiting valve with a falling characteristic curve is provided as pilot control valve, by means of which it is possible to adjust a control pressure which acts, together with the spring, on the valve body of the main pressure regulating valve in the direction of an increase of the delivery volume of a pump. In this way, an electrically actuated pressure regulating valve arrangement is created in which an increase of the current through an electromagnet effects a dissipation of the control pressure and thus a displacement of the valve body of the main pressure regulating valve in the direction of a reduction of the delivery volume, and thus of a reduction of the working pressure of the pump. Thus, the electrically actuated pressure regulating valve arrangement has a negative characteristic curve which, in the event of an electrical failure at the electromagnet, sets the set maximum pressure regulating value of the pump (failsafe).
A pressure regulator for a pump with a main pressure regulating valve and with an electromagnetically adjustable pilot-controlling pressure limiting valve with falling characteristic curve is also known from DE 43 29 164 A1.
A disadvantage of the latter electrically actuated pressure regulating valve arrangements is that the outlay in terms of apparatus and the installation space requirement are high because such arrangements involve a combination of the main pressure regulating valve and of the additional electrically actuated pilot-control valve.